POINT TRANSECT ESTIMATES OF RESIDUE COVER OR CROP CANOPY IN ROWS

Linear evenly spaced point transects are typically used to measure per cent of the soil surface covered by crop residue or canopy. As few as five 100-point count transects provide relatively precise measures of uniformly distributed cover but such transects can provide very poor p recision if used to measure cover lying in parallel rows. Highly varia ble counts can be expected if the target occupies evenly spaced parall el stripes with alternating high (80% or more) and low (20% or less) c ovet: Precise means (S.D. < 5%) of cover on striped surfaces can be ob tained with equally spaced point transects if both point spacing and t ransect angle relative to tillage or planting rows are custom-selected for each pow spacing. However no single equal point spacing or transe ct angle will provide precise cover estimates at all planter and tilla ge tool row spacings used in agricultural fields It is hypothesized th at nonuniform point spacings will allow estimates of cover that are in dependent of transect angle on striped surfaces. The hypothesis was te sted using the variance in counts of intersections between the point d istributions and regularly striped geometric patterns. The standard de viation of intersection counts from randomly spaced point transects ra nged between 5 and 10% cover; but was independent of transect angle an d row spacing. A sinewave-like point spacing also produced cover estim ates that were independent of transect angle and row spacing. The adva ntages of a sinewave pattern are the following: it is unique in contra st to the large number of possible random spacings, it can be used on any row spacing, and it usually provides a lower standard deviation th an that obtained from randomly spaced points. The sinewave pattern sha res with evenly spaced points the disadvantage that non-random points do not meet the strict requirements SOP statistical sampling. Randomly spaced point transects are recommended for percent cover estimates on fields with visible striping.